Generally, in the textile industry, nanofibers refer to fibers whose diameter is less than or equal to 1 μm, which is the limiting diameter of a conventional spinning process. The nanofibers can be produced by a variety of methods including drawing, template synthesis, self-assembly, chemical vapor deposition (CVD), phase separation, electrospinning, and hybridization of the conventional spinning process. Among these methods, electrospinning is a nanofiber manufacturing method that is in the most widely researched field in terms of mass productivity, handling properties, selection of various raw materials, wide application and processing, and that is in an early stage of industrialization through success of mass production and convergence with existing materials.
The electrospinning technique involves applying a high voltage to a polymer solution or melt and spraying the polymer solution onto a charged surface with a negative pole or earth, during which a solvent is volatized while nanofiber shaped materials are manufactured by being laminated in a web or non-woven state. Such a nanofiber web is a non-woven fabric composed of fibers having a diameter of less than 1 μm, and has a porosity of 60% to 90% and an average pore size of 0.2 μm to 1.0 μm according to the diameter and thickness of the fibers. However, nanofiber webs are generally poor in handleability when applied in industry, and have poor physical properties such as tension and tensile strength. Therefore, they are used in combination with existing materials to form secondary battery membrane materials, environmental purification filter materials, membrane materials for clothing, medical materials, etc. However, considering the inherent physical properties of the non-woven fabric made of nanofibers, it has been limited to be widely used for high strength materials and various application fields.
Therefore, when a filament yarn composed of nanofibers is manufactured, it is possible to manufacture a variety of secondary work pieces such as weaving, knitting, mesh, and rope, thereby greatly expanding the use of the nanofibers.
Synthetic or natural fibers are twisted to increase the strength of the yarn and to improve the weaving and knitting properties by imparting tactile, elastic, and bulk properties to the yarn. The synthetic fibers may be classified into mono filaments or multifilaments, and the natural fibers may be classified into low twist yarns to crepe hard twist yarns, depending on the material and the turns of twists, while imparting twists to the yarn in the form of spun yarns.
However, in the case of such synthetic fibers and natural fibers, the fibers are composed of several to several tens of micrometers in diameter, and are several ten times or several thousand times as thick as those of electrospun nanofibers. Therefore, when yarns are twisted in the same material and the same thickness, the nanofibers have a high porosity, so that the structures such as weaving and knitted fabric can be easily lightened and the contact area can be improved by using a high surface area. Therefore, the waterproof and breathable functions can be made convenient.
Therefore, when a composite false twist yarn made of nanofibers is manufactured, it becomes possible to manufacture various kinds of secondary work pieces or structures such as weaving, knitting, mesh, and rope, and thus the use of the nanofiber can be greatly expanded as a base material.
As a conventional technology relating to such a composite false twist yarn, Korean Patent Application Publication No. 10-2011-0047340 (Patent Document 1) discloses a method of producing a nanofiber composite yarn. In the case of Patent Document 1, a method of producing a nanofiber-containing nanofiber composite yarn has been proposed, in which a spinning web composed of polymer nanofibers having a fiber diameter of less than 1 μm is laminated by the technique proposed by the present inventor and then slitted to produce a nanofiber tape yarn, and then the nanofiber tape yarn is conjugated and twisted by a twisting machine. Patent Document 1 is conceptually limited to techniques for a method of manufacturing a nanofiber-only composite yarn and a method of producing a covering yarn.
The present inventor has completed the present invention by innovatively improving the manufacturing technology of the nanofiber composite yarn proposed in Patent Document 1 to improve the continuous productivity and practicality of the nanofiber-based false twist yarn, and by utilizing the advantages of lightweight, wide specific surface area, moisture permeability, water resistance, and functionalization of nanofibers and realizing the physical and chemical properties of existing materials simultaneously, via convergence of a nanofiber-only twist yarn and the conventional spinning yarn or synthetic fiber yarn.